This invention relates to a method and apparatus for maximizing the amount of lumber which can be used and still prevent chipout when finger joints are machined in the ends of pieces of lumber.
There are many applications where long continuous pieces of clear lumber are required, such as for molding and the like. These long pieces are obtained by finger jointing the ends of shorter pieces and gluing them together, since this process does not cause serious disfiguration on the face of the joined piece. Many of the shorter pieces used for this purpose are obtained by cutting knots or other imperfections out of longer pieces. When this occurs, determining how close to the imperfection the cut should be made is not easily ascertained. If the cut is made too close to the imperfection, local wood fiber deviation will be encountered and the corner of some of the raised portions between finger joint notches will break off, an occurrence which commonly is referred to as chipout. On the other hand, if the cut is spaced away from the knot usable lumber is wasted.
Growth ring patterns and fiber orientation are two separate and independent characteristics. Growth ring patterns, however, often can indicate areas of local fiber deviation. The term cross-grain is used to mean fibers that are not oriented parallel to the major axis of a piece of lumber. Because wood fibers are not individually visible to the naked eye, heretofore the decision where to make the cut has been determined by the person making it based on the visible growth ring pattern proximate a defect including a respectable margin for error. This method is clearly inefficient and does not permit the cut to be made as close to the imperfection as possible. Accordingly, a visual determination of where the cut will be made relative to an imperfection is very subjective, and, as a result, generally wasteful of lumber. Second, even where the visual growth ring pattern does reflect the fiber direction, it has been the prior art practice to place the cut in a location where the fiber direction is substantially parallel with the longitudinal axis of the piece of lumber and, as it happens, this practice causes a considerable amount of lumber to be wasted.
The present invention overcomes the shortcomings of the prior art method for determining where to make the cut when imperfections are being removed from pieces of lumber which are to have finger joints cut in their ends by making the cut immediately adjacent to the imperfection, and then orienting the piece of lumber prior to machining in a manner that will eliminate chipout regardless of the degree of cross-grain present. This requires that after the cut has been made the end of the board is scanned by a device which can detect the direction in which the fibers are oriented with respect to the longitudinal center line of the piece of lumber. The piece of lumber then is oriented prior to machining such that the angle between the tangent of the cutting circle of the finger joint cutter and the fiber direction is greater than or equal to 90.degree..
The apparatus for accomplishing this comprises a conveyor which transports the cut pieces of lumber normal to their longitudinal axes. A commercially available scanner, which is positioned above and below one end of the pieces of lumber, determines the direction of the fibers in each piece of lumber as it passes below the scanner and transmits this information along with the location of the piece of lumber on the conveyor to a microprocessor for storage.
Located downstream of the scanner is an orienter which is capable of rotating the pieces of lumber 180.degree. about their longitudinal axes upon command. The orienter is annunciated by the microprocessor to rotate each piece of lumber having its fibers angled to one side of its longitudinal axis and not to rotate any piece of lumber having its fibers angled to the other side of its longitudinal axis or parallel with it.
The final element of the apparatus of the present invention is a finger jointer which comprises a high speed rotating cylinder having a plurality of knives projecting from its periphery. The finger jointer is located downstream of the orienter and is positioned such that the knives cut into the ends of the pieces of lumber as the conveyor transports them past the cutters.
The pieces of lumber are positioned by the orienter such that the fiber direction at the ends which are to be machined are angled away from the finger jointer. Thus, the tangent of the cutting circle of the knives as they enter the pieces of lumber and the fiber direction always are offset from one another by 90.degree. or more.
Accordingly, it is a principal object of the present invention to provide a method for machining finger joints as close as possible to an imperfection which is located in a piece of lumber without the occurrence of chipout.
It is a further object of the present invention to provide such a method which permits machining of the finger joints in lumber having cross-grain.
It is a further object of the present invention to provide such a method in which the pieces of lumber are oriented such that the direction in which the knives of the finger joint cutter are moving is aligned as close to the fiber direction as possible when the finger joints are being machined.
It is a further object of the present invention to provide an apparatus for performing the foregoing method.
The foregoing and other objectives, features and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings.